Measurement of vibration with Young's fringe modulated speckle patterns in a photorefractive correlator

A technique has been proposed to analyze small in-plane component of vibrations by measuring the fringe shift, and analysing the correlation output of captured vibrating Young's fringes with a photorefractive correlator. Fringes are formed due to interference between the reconstructed speckled beam recorded for stationary object beam, and vibrated speckled beam transmitting through a BaTiO₃ crystal after introducing a small shift in the diffuser position. The correlation peak intensity is affected due to mismatch of vibrations between two piezo-mirrors in the object beam. High correlation output gives an indication of the frequency matching of known reference and unknown vibrations, thus giving information on the frequency of vibration. Vibration amplitudes of the order of a wavelength of light have been measured by counting the number of fringes passing past a line in the observation plane.     

光折变聚合物材料的研究进展

本综述了光折变聚合物材料的发展历史和现状。概括出了这种新型光折变材料的发展思路,并汇总了各种类型材料的光折变特性参数。     

光折变晶体中双光束耦合的解析解

光折变晶体中二波耦合过程也是全息记录的过程,本文将描述二波耦合的耦合波方程与描述光折变全息的Kukhtarev方程联立,基于Moharam的场函数,以光强调制度为主要变量,求得了适用于任意的干涉光强调制度及任意常量光激发效率下的耦合的两束光波在稳态时的解,进而得出热激发对光波耦合的影响。     

Ultraviolet photorefractive effect in Mg-doped near-stoichiometric LiNbO3

The ultraviolet photorefractive effect of Mg-doped near-stoichiometric LiNbO₃ crystals prepared by vapor transport equilibration (VTE) technique was studied at 351 nm. It was found in the near-stoichiometric LiNbO₃ crystals that the ultraviolet photorefractive effect could be enhanced greatly with the increase of Mg concentration. Based on the activation energy of dark decay of the photorefractive grating, possible centers responsible for the ultraviolet photorefractive effect were also discussed.     

Double optical waveguide in Cu-doped KNSBN crystal formed by MeV boron ion implantation

We reported for what is to be believed the first time a double optical waveguide in a Cu-doped potassium sodium strontium barium niobate (KNSBN) crystal formed by double boron ion implantation. The energy and dose of B⁺ and B³⁺ ions were (3+6) MeV and (2+2)×10¹⁴ ions/cm², respectively. The refractive index profile of the waveguide showed a double-barrier confined shape, which suggested the formation of a two-layer waveguide structure. The two waveguide layers were with thickness of 2.6 and 2 μm, respectively, which was in a good agreement with the parameters obtained from transport and range of ions in matter 98 (TRIM) code simulation. The nuclear energy loss distribution of the MeV B ions implanted into this crystal had a similar shape to that of the waveguide index profile, which means an inherent relationship between the waveguide formation and the energetic energy deposition.     

Manakov solitons in biased photorefractive polymer

The coupled equations for the incoherently coupled soliton pairs in biased photorefractive polymer are provided. It is shown that the coupled soliton equations reduce to Manakov equations when the total intensity of two coupled solitons is much lower than the background illumination. The bright-bright, dark-dark, and grey-grey soliton pair solutions of these Manakov equations are obtained, and the characteristics of these Manakov solitons are also discussed.     

一维标量光折变大光强、饱和光强空间灰孤子

推导出了光折变空间灰孤子在大光强和饱和光强条件下所满足的非线性波方程,并进行了数值求解,给出了大光强和饱和光强一维标量光折变灰孤子的复振幅空间分布。     

Temporal response of photorefractive multiple quantum wells in Franz-Keldysh geometry

Transient behavior of the photorefractive grating generated in multiple quantum well structure working in the transverse Franz-Kieldysh geometry is considered. Analysis was performed in the framework of the band transport model with material parameters of GaAs/AlGaAs system. The influence of carrier transport nonlinearity caused by the intervalley scattering of electrons was taken into account. An analytical expression for the grating formation time is derived and compared with numerical solutions as well as with the available experimental results. The results show that in the case of stationary interference pattern the nonlinear transport of electrons does not considerably improve the response time of the structure. This conclusion, checked for parameters used in majority of experiments, does not confirm the statements of earlier papers.     

Photoinduced effects in hybrid sol-gel materials

Hybrid silica-based sol-gel films containing Disperse Red 1 (DR1), carbazole units (CBZ) and 2,4,7-trinitro-9-fluorenone (TNF) at different concentrations show reversible photoinduced birefringence. Polarization sensitive holographic gratings have been produced and characterized. Dichroism measurements give information on the orientation mechanisms and on the aggregation of the dye molecules. The alignment of the DR1 molecules by corona poling is verified by second harmonic generation (SHG) and a moving grating technique is used to investigate an asymmetric energy exchange in a two-beam coupling experiment, typical of photorefractive gratings.     

Hydrothermal synthesis of organic hybrid BaTiO3 nanoparticles using a supercritical continuous flow reaction system

Barium titanate (BaTiO₃: BT) nanoparticles were synthesized by the hydrothermal method in the presence of dispersants using a continuous supercritical flow reaction system. The reactants of TiO₂ sol/Ba(NO₃)₂ mixed solution and KOH solution were used as starting materials and that was heated quickly up to 400 °C under the pressure of 30 MPa for 8 ms as reaction time. The dispersant solution such as polyacrylic acid (PAA) and polyoxyethylene(20) sorbitan monooleate (Tween 80) was injected in the cooling process after the reaction. The crystal phase of the obtained particles was identified as perovskite cubic BaTiO₃ by X-ray diffractometry (XRD) and Raman spectroscopy. Raman spectra and thermogravimetric data revealed that PAA and Tween 80 fabricated hybrid BT nanoparicles. Primarily particle size of the BaTiO₃ nanoparticle was determined by means of BET surface area, as small as less than 10 nm irrespective of dispersants. In contrast, dispersed particle size in solution measured by dynamic light scattering (DLS) technique decreased from 282 nm to less than 100 nm depending on the dispersant. Aggregation of BaTiO₃ nanoparticles might be depressed in the presence of dispersants, especially PAA is the most effective among the dispersants examined.